The function and structure of two (possibly related) lymphokines, IL-6 and TAF, will be analyzed. By exploiting homology with a human probe, a murine IL-6 cDNA will be cloned and expressed, and monoclonal antibodies reactive murine IL-6 will be prepared. The functions of murine IL-6 and TAF will be explored by analysis of expression of the gene, secretion of active lymphokine, determination of target cells, determination of producer cells, identification of the receptors for the lymphokines, and studies of the effects of reactive monoclonal antibodies on T cell responses. The possible structural relationship of IL-6 and TAF will be explored.